Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for an image pickup apparatus using a solid-state image pickup element, such as a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera, or an image pickup apparatus such as a silver-halide film camera.
Description of the Related Art
In recent years, as an image pickup optical system to be used in an image pickup apparatus using a solid-state image pickup element, a zoom lens is required to have a short total length, be compact (small in size), and have a high zoom ratio (high zoom ratio) as well as a high resolution. As a zoom lens that satisfies those requirements, a positive-lead type zoom lens in which a lens unit having a positive refractive power is arranged on an object side has been known. As the positive-lead type zoom lens, a zoom lens including four lens units or five lens units as a whole has been known.
In Japanese Patent Application Laid-Open No. 2013-120326, a zoom lens having a four-unit configuration including, in order from an object side to an image side, a first lens unit to a fourth lens unit having positive, negative, positive, and positive refractive powers is described. The second lens unit and the fourth lens unit are configured to move during zooming, and the fourth lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2012-88603, a zoom lens having a four-unit configuration including, in order from an object side to an image side, a first lens unit to a fourth lens unit having positive, negative, positive, and positive refractive powers is described. The second, third, and fourth lens units are configured to move during zooming, and the fourth lens unit is configured to move during focusing.
In Japanese Patent Application Laid-Open No. 2007-328306, a five-unit zoom lens including, in order from an object side to an image side, a first lens unit to a fifth lens unit having positive, negative, positive, positive, and negative refractive powers is described. The second lens unit and the fourth lens unit are configured to move during zooming, and the fourth lens unit is configured to move during focusing.
In recent years, the zoom lens to be used in the image pickup apparatus is strongly desired to have the high zoom ratio and be small in size as the entire system in order to adapt to the downsizing of the image pickup apparatus. The above-mentioned positive-lead type zoom lens is relatively easy to downsize as the entire system and realize the high zoom ratio. However, in the above-mentioned positive-lead type zoom lens, in order to realize the high zoom ratio while further downsizing the entire system, it is important to appropriately set lateral magnifications of the respective lens units.
For example, in order to realize the high zoom ratio while downsizing the entire system, it is important to appropriately set lateral magnifications of the second lens unit at a wide angle end and a telephoto end, which mainly varies a magnification. When the lateral magnifications of the second lens unit at the wide angle end and the telephoto end are not appropriate, it becomes difficult to attain the high zoom ratio while downsizing the entire system.
Moreover, in realizing the high zoom ratio, when a lateral magnification held by the second lens unit at the time of varying the magnification is not appropriately set, the effect on a change in back focus with respect to a movement amount of the second lens unit in an optical axis direction is increased near the telephoto end, that is, a so-called focus sensitivity is increased. As a result, it becomes difficult to control zooming by moving the lens units near the telephoto end. For example, in a zoom lens for a monitoring camera, which is required to realize the high zoom ratio, it is important to appropriately set the lateral magnification held by the second lens unit during varying the magnification, and reduce the focus sensitivity of the second lens unit at the telephoto end.